Rudi Bertocchi

Experimentally Determined Optical Properties of a Polydisperse Carbon Black Cloud for a Solar Particle Receiver

Measured physical and optical properties of a stable polydisperse carbon black particle cloud at 532 nm and 1064 nm are reported. The particle cloud consisted of 99.7% spheroid primary particles (45‐570 nm diameter) and 0.3% large irregularly shaped agglomerates (1.2‐7.25 mm equivalent diameter). Although the numerical fraction of the agglomerates was only 0.2%, they contributed 60% to the cloud’s scattering cross section. The extinction coefficient, scattering coefficient and the scattering phase function were measured for both parallel and perpendicular polarized radiation at linear extinction coefficients ranging from 0.6 to 4.1 m 21 . The cloud exhibited strong forward scattering, with 62% of all scattered energy in a forward lobe of 15° at 532 nm and 48% at 1064 nm. The scattering albedo was measured to 35% at 532 nm and 47% at 1064 nm. The dimensionless extinction coefficient was measured to 8.25 at 532 nm. The experimental data was compared to standard Mie theory by integrating the weighed contribution based on particle size, including agglomerates, according to the detailed measured population distribution. Neglecting the contribution of the agglomerates to the cloud’s optical properties was shown to introduce discrepancies between Mie theory and measured results. The results indicate that the-Mie theory can be used for estimating the optical properties of a partially agglomerated carbon black particle cloud for simulation of a solar particle receiver. @DOI: 10.1115/1.1756924#

Carbon Particle Cloud Generation for a Solar Particle Receiver

The development and performance of a full-scale carbon particle cloud generator together with the evaluation of nine commercial carbon blacks is reported. Large variations were found in the dispersability and settling properties of the investigated powders. Scanning electron microscope analysis of cloud samples from different powders showed unequal state of agglomeration and particle size. The particle population distribution of the most suitable powder was determined, showing that the particle cloud consisted of 99.8% spheroid primary particles (25-570 nm dia) and 0.2% large irregularly shaped agglomerates. Although the numerical fraction of the agglomerates was only 0.2%, they contributed 40% to the clouds geometrical cross section. Significant variations in the population distribution were found from different batches of the same particle powder The developed full-scale particle generator was capable of sustained operation, creating a particle cloud with an extinction coefficient exceeding 40 m -1 at a nominal flow rate of 25 SLPM. The dispersal efficiency of the system with the optimal ejection nozzle was 25%, compared to less than 1% for free ejection. The particle dispersal rate was 30 g/hr at 25 SLPM at an evacuation efficiency of 87%. Specific extinction cross-sections of 5.8 m 2 /g were measured for particle mass loading higher than 2 g/m 3 .

A High Temperature Solar Particle Receiver

A solar particle receiver was developed to heat a process gas to very high temperatures. Its operation is based on seeding the process gas with a very large numerical amount ~but small mass fraction, less than 0.5%! of sub-micron radiation absorbing particles ~see article by Bertocchi et al. in this issue!. The gas-particle mixture is exposed to highly concentrated solar energy in the receiver. Peak temperatures obtained were 2,100 K with Nitrogen, and 2,000 K with air. Radiation to thermal energy conversion efficiencies were estimated to exceed 85%. The receiver accumulated 12 hours of operation at temperatures over 1,700 K without major failure @1#.

Solar Fixation of Atmospheric Nitrogen

The thermal fixation of atmospheric nitrogen is explored, using a recently developed concept of a particle-seeded solar receiver. The thermodynamics and the kinetics of the formation of nitric oxide (NO) in air at temperatures of about 2300 K are analyzed, and the required residence time and the time to reach the steady state of the reaction between nitrogen and oxygen are calculated. The novel particle-seeded receiver concept is briefly described. The adaptation of the particle-seeded receiver to the fixation reaction in terms of heating rate of the air and residence time is validated based on previous test results and complementary calculations. A proposed method where the solar receiver/reactor is simultaneously coupled with power production, using the exhausted hot air from the reactor to generate electricity, is described. This concept can definitely increase the economical benefit of the process and, thus, its potential attractiveness. Some illustrative figures for a commercial size system are provided.